JavaScript Object Reference and Promise.allSettled() Method Quiz

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Questions and Answers

What is the purpose of React.Fragment in React?

To create a reusable component

To group multiple children elements without adding extra nodes to the DOM (correct)

To define a new context for child components

To handle form inputs

In React, what is the purpose of the key prop when rendering a list of components?

It is used to uniquely identify each child element in a list (correct)

It specifies the styling for each child element

It defines the structure of the child components

It determines the order in which the elements are rendered

What is the purpose of React.memo in React functional components?

To memoize the component's state

To memoize the component's props

To memoize the component's context

To memoize the component's rendering (correct)

In React, when should you use a controlled component instead of an uncontrolled component?

When the input value is controlled by React state Signup and view all the answers

How does React optimize rendering performance when updating the DOM?

By using virtual DOM Signup and view all the answers

What is the purpose of the useReducer hook in React?

To manage complex state logic in a cleaner way Signup and view all the answers

What will be logged to the console when the following code is executed? `const a = { key: 'value' }; const b = a; b.key = 'updated value'; console.log(a.key);`

'updated value' Signup and view all the answers

Which of the following is true about JavaScript's `Promise.allSettled()` method?

It waits for all promises to be settled (either resolved or rejected) Signup and view all the answers

What does the `Symbol` datatype represent in JavaScript?

Unique and immutable values Signup and view all the answers

When using the `await` keyword within an `async` function in JavaScript, which of the following is true?

The <code>async</code> function pauses execution until the awaited promise is resolved or rejected Signup and view all the answers

What will be the output of the following code? `const value = Promise.resolve(5); console.log(typeof value);`

'object' Signup and view all the answers

In React, which lifecycle method is invoked immediately after a component is inserted into the DOM?

componentDidMount() Signup and view all the answers

Study Notes

React Lifecycle Methods

componentDidMount() is invoked immediately after a component is inserted into the DOM

React.Fragment

Purpose: to group multiple children elements without adding extra nodes to the DOM

React Key Prop

Purpose: to uniquely identify each child element in a list when rendering a list of components

React.memo

Purpose: to memoize the component's props in functional components

Preventing Component Rerender

Use shouldComponentUpdate lifecycle method or React.memo to prevent a React component from rerendering when its parent re-renders

Controlled vs Uncontrolled Components

Use controlled components when the input value is controlled by React state or when the form is dynamic

React Hooks

Allow you to use state and other React features without writing a class
Can be used for managing state, handling side effects, and more

React Rendering Optimization

React optimizes rendering performance by using a virtual DOM

useEffect Hook

Purpose: to perform side effects in function components

useReducer Hook

Purpose: to manage complex state logic in a cleaner way

JavaScript Objects and References

When you update a copied object, the original object is also updated because objects are references

JavaScript Promises

Promise.allSettled() waits for all promises to be either resolved or rejected

JavaScript Symbol Datatype

Represents unique and immutable values

Async/Await in JavaScript

When using the await keyword, the async function waits for the awaited promise to resolve or reject

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Description

Test your knowledge on JavaScript object reference and the Promise.allSettled() method. Determine what will be logged to the console in a given code snippet, and understand the behavior of Promise.allSettled().